Conventionally, a switching hub device has been known that has a function to detect duplication of an IP address, by receiving data at ports to obtain IP addresses of respective devices connected at the ports, and by recording correspondences between the ports and the IP addresses set to the devices connected at the ports.
The switching hub device has a function that obtains an alternative IP address that is not being used for the devices connected at the ports if detecting duplication of an IP address, and assigns the alternative IP address to the port at which the duplication of the IP address is detected. The switching hub device also has a function that if the port having the alternative IP address assigned receives data, the function converts the IP address of the source device that transmits the data to the alternative IP address assigned to the reception port. The switching hub device also has a function that if transmitting data to the port having the alternative IP address, the function converts the destination IP address of transmission data to the IP address corresponding to the transmission port.